Method and apparatus for forming features in cans

ABSTRACT

A method and apparatus for mechanically reshaping and/or forming textured features in the side wall of metal can bodies in which a can body is mounted on a profiled mandrel and rolled along a second mandrel or rail, which is also profiled. The tools are made from hard material but the second mandrel or rail is resiliently mounted. This mounting has been found to facilitate control of the depth of the profiled features formed in the can body. In particular, the problem of depth variability which will arise due to expansion of the machine and tooling in normal running conditions, or variability in thicknesses in the can body is avoided. Typically, the can body is clamped between complementary unformed regions on the tools during forming so as to prevent wrinkling or localised thinning of the can side wall.

BACKGROUND OF THE INVENTION

This invention relates to a method and apparatus for forming features incans. In particular, it relates to a method and apparatus formechanically reshaping and/or forming textured features in the side wallof metal can bodies.

It is known for example from EP-0492860 that features such as flutes canbe formed in the side wall of can bodies by rolling the can, supportedon a hard profiled mandrel, along a flexible rail of polyurethane. InEP-0492860, the profile of the mandrel comprises a whole number offlutes which is less than the number of flutes on the finished can body.

EP-0731740 describes another apparatus for forming grooves such asflutes in a can side wall. The apparatus of this application uses a railhaving hard profiled features, the can body being carried by a mandrelof softer resilient material such as polyurethane.

EP-0492860 also describes the use of a rail and mandrel, both of whichare made from hard material. The rail is fixed in position and very fineclearance and accurate matching of forming depth between the mandrel andrail must be maintained for the flutes to be formed. It is not feasibleto maintain these in practice due to the increase in temperature andmachine and tool expansion which occur during normal running conditions.Typically a rise of up to 40° C. is found when operating at 500cans/minute and a temperature rise of 50° C. has been found whenoperating a beader at 1500 cans/minute. Since compensation for thistemperature rise is not possible, damage to the machine can occur.

A roll forming apparatus such as that described in EP-0492860 uses arotating turret to carry a number of heads comprising profiled mandrels,each of which is rotatably mounted on the turret on shafts. As theturret rotates, the can bodies located on the profiled mandrels areengaged between a profiled mandrel and a profiled rail. The shafts ofthe mandrels are driven so that cans mounted on the mandrels are rolledalong the rail. The radial position of the mandrels on the turret is setprior to operation. However, if there is mis-setting of the heads, thiswill lead to variation in the depth of profiles formed on the cans whichmay be unacceptable to the customer.

It should be noted that temperature rise leads primarily to turretgrowth and subsequent change in profile depth. This in turn will resultin a change in can performance. If the heads have been incorrectly set,then the problem is exacerbated still further.

Another profile commonly provided for food cans is beading. Beadingtypically comprises one or more clusters of circumferential beads whichimprove can panel performance (i.e. radial strength when subjected toexternal pressure) particularly during thermal processing. Beads aregenerally formed by rolling the can body between a rotating mandrel anda fixed rail, or a pair of rotating mandrels. Both tools areindependently mounted and located on separate assemblies. However, asthe temperature of the machine and tooling increases during normaloperation, the depth of the beads varies and cans with unacceptable beaddepths made during the warm up period may be rejected. Conventionalbeaders have been found to exhibit up to 0.1 mm (0.004″) depth growthwhen hot. One beader, operating at 1500 cans/minute was found to exhibitup to 0.18 mm (0.007″) depth growth.

Variation in depth on beading machines has become more of an issue asthe industry is continually striving to produces thinner lightweightcans. Previously, body thickness was high enough to absorb changes inbead/profile depth resulting from poor machine settings and temperaturevariation. This is no longer the case.

None of the prior art documents addresses or even recognises the problemof control of the depth of the profiled features formed in the can body.In particular, the problem of depth variability which will arise due toexpansion of the machine and tooling in normal running, poorly setheads, or variability in thicknesses in the can body, has not beenpreviously been addressed. This invention seeks to provide a solution tothat problem.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides an apparatus for formingfeatures in the side wall of cylindrical metal can bodies, the apparatuscomprising: first and second tools formed from hard material and havingcomplementary profiles, one of the tools being adapted to carry a canbody; means for rolling the first tool relative to the second tool todeform the side wall of the can body between the tools; and a resilientmounting for the second tool for biasing the second tool towards thefirst.

By resiliently mounting the second tool, a series of cans may be formedwith identical features of texture or shape, the features havingconstant depth or the same depth variations, depending on the desiredprofile. Unlike prior art apparatus, where the tools are independentlymounted, in the present invention movement of the first tool is thusaffected by movement of the resilient mounting of the second.Consistency between a series of cans, or different batches of cans canthus be guaranteed, irrespective of environmental conditions, can wallthickness, head to head variation etc. The depth is thus set by thetooling profile rather than by the relative position or spacing setbetween the tools as in known forming apparatus. In order that thesecond tool exerts a positive biasing force towards the first tool, thebiasing load should exceed the forming load, i.e. the load exerted todeform the can side wall.

Usually, the tool which carries the can will be a mandrel. The othertool may be either a second mandrel or a rail. The second, resilientlymounted tool may either be provided by the tool carrying the can or bythe cooperating tool in the form of a second mandrel or rail. When thesecond tool is a rail, this rail may be pivotally mounted. This isparticularly useful since more than one can/mandrel may be on the railat any one time.

In a preferred embodiment, each tool includes complementary unformed(unprofiled) regions such as plain edge bands between which the can bodyis clamped during forming. This clamping will support the can body inthe unformed areas and spread the load over a larger area so as toprevent wrinkling or thinning of the can side wall. To avoid thinning inbeading operations, the bead profile may also have to be adjusted. Toolto tool contact for clamping contrasts from, for example, known beaderswhere a gap between the tooling is always maintained so that there is nodirect contact which could lead to pinching and localised thinning ofthe can wall.

Alternatively, in some texturing applications, where the texturedfeatures are not continuous along the length of the rail or around thecircumference of the mandrel, the can body may be clamped between thetools in the regions which are not being formed.

Where clamping takes place beyond the edges of the profile only, theapparatus may further comprise means for adjusting the depth of thetextured feature. Typically, this depth adjuster may comprise a spaceron a profiled rail for raising the clamped region relative to theprofiled part of the rail. Where a secondary mandrel is used, a pair ofrings may be used to adjust the depth. Depth adjustment may also be usedto compensate for wear of tool parts.

A preferred embodiment of the invention will now be described, by way ofexample only, with reference to the drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side section of a can mounted on a mandrel moving onto aforming rail;

FIG. 2 is the section of FIG. 1, with the can rolling along the formingrail;

FIG. 3 is a transverse section of the rail and mandrel of FIGS. 1 and 2,showing the can clamped between the mandrel and rail;

FIG. 4 is the section of FIGS. 1 and 2, showing the can clamped betweenthe mandrel and rail; and

FIG. 5 is a plan view of a can on the rail of FIGS. 1 to 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The embodiment shown in FIGS. 1 to 5 is similar to a roll formingapparatus such as that described in EP-0492860 which uses a rotatingturret to roll can bodies along a profiled rail. However, in EP-0492860,where hard tooling is used both for the mandrel and the rail, a fineclearance is always set between the tools so as to avoid localisedpinching of the can body between the mandrel and the rail.

In previous forming apparatus, where the profiled rail is made fromflexible material such as polyurethane, the flexible rail material islocally deformed by the action of the mandrel. Soft polyurethanematerial has reduced operating life in comparison with hard rails and,ultimately, unwanted variations in the texture or shape of the finishedcan will arise.

Use of a hard mandrel and hard (“solid”) rail as described in EP-0492860requires very accurate matching of forming depth. In particular, thereis nothing to compensate for temperature variation resulting invariation in the depth of features formed on the can side wall. Althoughthe heads can be wound radially outwards, a constant tool gap cannot bemaintained when the temperature of the machine and tooling increasesduring normal running conditions.

FIG. 1 shows a can 5 mounted on a profiled mandrel 10 and rolling onto aforming rail 20. The mandrel is made of hard material, typically metal,and has profiled flutes 15 around its circumference. The rail 20comprises a metal layer 25 which includes profiled features,complementary in shape to those on the mandrel, on its surface 30.

In contrast with prior art roll forming apparatus, however, the formingrail 20 of FIG. 1 is resiliently mounted, for example on springs 35, 40which bias the profiled rail outwards. Excessive outward movement of therail is prevented by flanged stops 45 on adjacent smooth rails 50.

By using hard tooling both for the mandrel and the rail, material wearis minimised. However, in contrast with earlier apparatus, accuratematching of tool depth is not essential since the resilient mounting ofthe tooling of the present invention will compensate for temperature andhead setting variations and will maintain desired forming depthsirrespective any such changes.

In FIG. 1, it can be seen that the forming rail 20 is pushed outwards bysprings 35 and 40, the movement being limited by the stops 45. As thecan and mandrel roll off the smooth rail 50 onto the forming rail, theforming rail is pushed away from stop 45 by the mandrel, and spring 40is compressed, as shown in FIG. 2. Movement of the springs depends onany temperature change, head setting, can thickness variation and/ortooling depth variability. The provision of springs thus compensates forany of these undesirable features, even if these are within specifiedtolerances. It will be appreciated that in addition to resilientlymounting the rail 20 so that it can move to maintain desired formingdepths around the circumference of a can (as shown in FIG. 1), the rail20 may also be resiliently mounted so that it can move in aperpendicular direction, to maintain the desired forming depths alongthe length of the can.

FIGS. 3 to 5 demonstrate how localised pinching of the can body isfurther avoided using the apparatus of the present invention. The spring40 is still compressed as the can and mandrel roll from right to leftalong the forming rail 20 as shown in FIG. 4. As is best seen in theenlarged features of FIG. 3 and 4, the profile of the mandrel 10 andmetal layer 25 match in the plain regions, so that the can body isclamped along its length in these unprofiled regions between the mandreland rail However, since there are plain regions 55, 60 either side ofthe fluted profiles 30, 15 on the rail and mandrel respectively, theseregions will also clamp and support the can, thus preventing pinching ofthe can side wall.

Although in the embodiment shown, the can body is clamped between themandrel and rail either side of the flutes as well as beyond their ends,this is not always feasible, for example for beading operations. Inthese circumstances, it is important to have clamping beyond the beadprofile to avoid localised metal thinning and prevent depth variations.

In the embodiment shown, the profiled mandrel 10 has depressions acrossits surface which cooperate with projections on the rail 20, producing acan with depressions in the side wall. It will be appreciated that themandrel 10 could equally be provided with projections across itssurface, which co-operate with depressions in the rail 20, to produce acan with embossed features in the side wall. This arrangement isparticularly useful for producing embossed text and external threads orlugs on a can side wall.

The embodiment shown produces a can having longitudinal flutes along itsside wall. However, it will be appreciated that the tooling may also beused for a variety of other features in the can side wall such as logos,enhancing print or decoration, beading, embossing and creating threadprofiles. Such features are considered to be within the scope of theinvention as defined by the claims.

We claim:
 1. An apparatus for forming the side wall of a substantiallycylindrical can body comprising first and second tools formed from hardmaterial and having complementary profiles, said first tool beingadapted to carry a can body, means for rolling the first tool relativeto the second tool for deforming the can body side wall between thetools, means for resiliently biasing the second tool toward the firsttool, and said first and second tools include complementary unformedregions between which the can body side wall is clamped during forming.2. The apparatus as claimed in claim 1 in which the first tool is amandrel.
 3. The apparatus as defined in claim 2 in which the second toolis a mandrel.
 4. The apparatus as defined in claim 3 in which thecomplementary unformed regions are located at axially opposite ends ofthe first and second tools.
 5. The apparatus as defined in claim 2 inwhich the second tool is a rail.
 6. The apparatus as defined in claim 5in which the complementary unformed regions are located at axiallyopposite ends of the first and second tools.
 7. The apparatus as definedin claim 2 in which the second tool is a pivotally mounted rail.
 8. Theapparatus as defined in claim 2 in which the complementary unformedregions are located at axially opposite ends of the first and secondtools.
 9. The apparatus as defined in claim 1 in which the second toolis a mandrel.
 10. The apparatus as defined in claim 1 in which thesecond tool is a rail.
 11. The apparatus as defined in claim 1 in whichthe second tool is a pivotally mounted rail.
 12. The apparatus asdefined in claim 1 in which the complementary unformed regions arelocated at axially opposite ends of the first and second tools.
 13. Amethod of forming the side wall of a substantially cylindrical can bodycomprising the steps of providing first and second tools from hardmaterial and having complementary profiles, rolling the first and secondtools relative to each other to deform the can body side wall betweenthe tools, resiliently biasing the second tool toward the first tool,and clamping the can body at least between complementary unformedregions of the tools during forming.
 14. The method as defined in claim13 wherein the clamping takes place at axially opposite ends of thetools.